Pathogens & Contaminants

Executive Summary

A wide range of substances can drastically harm both public health and the environment. Hazardous substances that might be present in drinking water mainly include pathogens (microorganisms) and contaminants (inorganic chemicals, organic chemicals and metals).
Contamination of drinking water with pathogens including bacteria, viruses, parasitic protozoa and helminths is the major factor for prevalence of diseases in developing countries. Faeces infiltrating drinking water sources are most often responsible for contamination with pathogens.
Likewise, contaminants in drinking water originating from both human activities (anthropogenic) and natural processes (geogenic) incorporate large health risks depending on their concentration.

Sources and Dispersion of Pathogens and Contaminants

Sources of Pathogens and Contaminants

All waters (i.e. surface water, groundwater/aquifers) can become contaminated from many types of human activities as well as from natural sources. Agricultural, commercial, industrial, and residential development can all contribute to groundwater contamination (WALLIN 1997).

Potential rural contamination sources. Source: BUCHANAN et al. (2010)

Examples of activities that could negatively affect groundwater if not managed properly include:

Dispersion of Pathogens and Contaminants

Contaminants percolate permeable soil layers together with infiltrating water. Once reaching groundwater level, they spread not only horizontally but usually also vertically throughout the whole groundwater body (WAL 2010).

Migration of contaminants in an unconfined (left) and a confined (right) aquifer. Source: WAL (2010)

The concentration of most pathogens (but not necessarily chemicals) decreases gradually with depth as they are decomposed. Hence, in unconfined aquifers or if a confined aquifer is beyond the reach of available drilling technologies, wells should be drilled as deep as possible (WAL 2010). In a confined aquifer, the impermeable layer prevents contaminants from further vertical migration into the underlying aquifer making groundwater below this layer free from surficial contamination. As a consequence, confined aquifers generally are less susceptible to contamination (WAL 2010).

While soluble contaminants (e.g. pathogens, water-soluble contaminants, heavy metals, etc.) mix with groundwater, insoluble contaminants (e.g. oil or many solvents like trichloroethene (TCE)) do not mix with or dissolve as easily. Consequently, they accumulate either on the groundwater level or at the top of an impervious layer depending on their density.

Movement of insoluble contaminants in ground water. Left: Oil spills (lighter than water) accumulate on the water table and spread horizontally. Right: Insoluble contaminants being heavier than water seep down until they reach impervious layers where they spread horizontally. Adapted from FREEZE et al. (n.y.)

General Effects of Pathogens and Contaminants

Drinking water contamination result in poor drinking water quality and can cause a loss of a community’s drinking water supply, high restoration costs, high costs for providing alternative drinking water supplies, and a high potential for community health problems. Additionally, contaminants can adversely affect environmental systems and causing the provision of ecosystem functions to fail.

Pathogens (Microorganisms)

Waterborne or excreta related diseases are still significant causes of mortality and morbidity in many developing countries. The transmission routes of these and the health risk factors involved are important, in order to design and implement or modify excreta use schemes so that the transmission of these diseases are reduced (see also health risk management). The pathogens of concern for environmental transmission through faeces mainly cause gastrointestinal symptoms such as diarrhoea, vomiting and stomach cramps. Several may also cause symptoms involving other organs and severe sequels or be an interrelated factor for malnutrition. Major pathogens may be viruses, bacteria, parasitic protozoa, and helminthes. The table below summarises the most common organisms in each category and the signs and symptoms or disease associated with them:

Example of pathogens that may be excreted in faeces (can be transmitted through water and improper sanitation) and related diseases, including examples of symptoms they may cause. Source: STENSTROEM et al. (2010); adapted from OTTOSON (2003)

All infections related to faeces are likewise representative for anal cleansing and ablution water. Infections related to faeces have traditionally been centred on enteric pathogenic bacteria. In developing countries with insufficiently functioning sanitation systems, outbreaks of cholera, typhoid and shigellosis still are of major concern. Among the bacteria, at least Salmonella, Campylobacter and Enterohaemorrhagic E. coli (EHEC) are of general importance, both in industrialised and developing countries, when microbial risks from various fertiliserproducts are considered, including faeces, sewagesludge or animal manure.

The Ganges River, where a lot of untreated sewage is disposed in, is one of the most heavily polluted rivers on the earth. Source: CONRADIN (2004)

Environmental Risks of Faeces, Urine and Greywater

More than 120 different types of viruses may be excreted in faeces, including members of the enteroviruses, rotavirus, enteric adenoviruses and human caliciviruses (noroviruses) groups. Hepatitis A is also of major concern and the importance of Hepatitis E is emerging, when applying wastes to land and is considered a risk for both water- and food- borne outbreaks, especially when the sanitary standard are low.

The parasitic protozoa, Cryptosporidium and Giardia are occurring with high prevalence as an enteric pathogen. Entamoeba histolytica is also recognised as an infection of concern in developing countries. Others like Cyclospora and Isospora may also be of concern.

In developing countries, geohelminth infections are of major concern. The eggs (ova), of especially Ascaris and Taenia are very persistent in the environment. Hookworm disease is widespread in most tropics and subtropics areas, and affects nearly one billion people worldwide. These infections exaggerate malnutrition. The eggs from Ascaris and hookworms that are excreted in the faeces require a latency period and favourable conditions in soil or deposited faeces to hatch into larvae and become infectious.

Schistosoma haematobium are excreted both in faeces and urine while other types of Schistosoma, e.g. S. japonicum and S. mansoni are just excreted in faeces. More than 200 million people are currently infected with Schistosomiasis. The use of treated excreta should not have an impact but fresh or untreated faecal material, which should not be used, constitute a risk when applied close to fresh water sources where the snail is present.

Environmental transmission of urinary excreted pathogens is of limited concern in temperate climates, but any faecal cross-contamination that may occur by misplacement of faeces in the urine-diverting toilet ends up in the urine fraction and is a determinant of possible health risk. Also in tropical climates, faecal contamination of collected urine may be considered as the greatest risk but some urinary-transmitted pathogens also need to be considered. The pathogens excreted in urine are Leptospira interrogans, Salmonella typhi, Salmonella paratyphi and Schistosoma haematobium. There is a range of other pathogens, including some of the human viruses that have been detected in urine but their presence may normally be considered insignificant for further risk of environmental transmission.

The main hazard of greywater is, as for urine, due to faecal cross-contamination. Faecal contamination is limited in amounts when one is considering the traditional fractions of greywater, like washing faecally contaminated laundry (i.e. diapers), childcare and showering. If anal cleansing is combined in greywater the risk is enhanced. In many situations, other sources of faecal contamination in greywater occurs, but is often forgotten or not considered in a system perspective. In reality, these will be the main drivers for the subsequent microbial health risks.

Transmission of Diseases

The infectious organisms are released from the bodies of infected persons in their excreta, eventually reaching other people, that may be infected via either the mouth, for example when being in contact with contaminated areas and accidentally transmitting minute quantities to the mouth, when contaminated crops are eaten or when drinking contaminated water) or through contact with the skin (e.g., hookworm and schistosomiasis) or through inhalation of contaminated aerosols or particulate material.

The relative importance of these pathogens in causing illnesses depends in addition on a number of factors including their persistence in the environment, minimum infective dose, ability to induce human immunity, and latency periods (SHUVAL et al. 1986). Thus pathogens with a higher probability of causing infections are those that:

Have long persistence in the environment.

Have low minimal infective doses.

Elicit little or no human immunity.

Have long latency periods.

The amount and variability of the pathogens will depend mainly on the infection among the population served and the scale of the sanitation system (see also health risk management). Thus, in low income countries, where there is a high prevalence of excreta related diseases, a greater number of pathogens are more likely to be introduced into a sanitation systems, compared to a developed countries where the prevalence of such diseases is generally low (see also toilet systems).

Incidence Rate of Diseases

The incidence rate of a disease is the yearly number of reported cases divided by the total population, often expressed per 100 000 people. The incidence will vary due to the prevailing epidemiological situation within an area. The reported number of cases is often substantially underestimated and pathogens causing less severe symptoms are less likely to be reported. The disease incidence and excretion factors will, in general terms, give their concentration at the time of excretion and the subsequent risks will relate to environmental persistence and die-off, dilution factors, exposure and the dose that humans are exposed to. The later further relate to the efficiency of technical and behavioural barriers within the system context (see also health risk management).

Contaminants

Inorganic chemicals comprise some of the most common and mobile contaminants in groundwater. Such contaminants include nitrate, ammonia, sodium, chloride, fluoride, and arsenic. Nitrate contamination from sewage and agricultural practices occurs over large areas. Salt in groundwater can be the result of the upwelling of highly mineralised geothermal or sea water in coastal areas, and road de-icing. Fluoride and arsenic can occur naturally in areas containing sediments derived from igneous rocks. Nitrate and chloride do not adsorb readily on to soil materials and can be transported great distances.

Organic compounds are carbon and hydrogen-based chemicals, some of which occur naturally. However, it is mainly the human-produced chemicals that are of concern. These chemicals include solvents, pesticides, and other industrial chemicals. Organic chemicals are removed from groundwater by chemical reactions and microbial activity. Many organic compounds, however, particularly those containing chlorine, can remain in the subsurface for many years. Many organic chemicals are highly toxic and cause severe health problems such as birth defects and cancer.

Metals, including heavy metals, are also of environmental concern. The transport of metals is controlled by their solubility. The solubility of metals is dependent on pH. The pH of water can be affected by acid drainage from mining activities. Dissolved metals can also be adsorbed onto large organic molecules in water and be transported by them.

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